An important aspect of dental restorations is the accurate shade matching of the shade of the restoration work to the natural teeth of a patient. Such matching can be difficult because natural teeth often have different optical properties than restorative materials. In particular, teeth exhibit the properties of translucency, opalescence, and fluorescence whereas restorative materials, such as dental porcelain, react to light differently depending on the underlying material such as zirconia, lithium disilicate, porcelain fused to metal or pressed ceramics are generally opaque and do not transmit light although they reflect and absorb it. Thus, matching an artificial restoration to natural teeth is as much art as it is science, encompassing a combination of clinical skill, experience, shade matching systems, and lighting conditions.
The traditional method for shade matching consists of visually comparing a shade tab to a tooth. Such shade tabs are fundamental tools used to communicate information in order to match color in the manufacture of prosthetic teeth, crowns, inlays, and similar products. The selection of a match, when using shade tabs, is a subjective choice done by eye. The information is written down on a lab form and communicated to the lab ceramist. Sometimes a picture of the tooth with the shade tab is made and also communicated. Opportunities for inaccuracies are inherent when conducting visual comparisons using shade tabs. Examples of sources that cause inaccuracies are eye fatigue, improper lighting, genetics and similarities among shade tabs. Also, once manufactured, there is no good way, other than a try-in with the patient, to determine if the restorative work will match. This is not only frustrating, but also a waste of time and money for the doctor, patient, and dental laboratory. Even when a tooth does not match, the corrective factor is not always easily determined.
Ideally, the clinician will convey the primary tooth shade characteristics of hue, chroma, and value to the technician, so that he or she may match the work to the remaining teeth. Hue refers to the wavelength of observed radiant energy, chroma describes the saturation of the hue, and value describes a color's relative darkness. Value is often the most important dimension of shade because it is noticeable if this parameter is off by just a small amount.
A photograph of the tooth adjacent to a shade tab can provide useful information to a technician. Editing software can be used to compensate for the color errors in digital photographs by conducting a color transformation in accordance with color references. Such references can contain the shade tabs of a shade system along with black, white, and gray. Although editing software can transform the depiction of color in a photographic image, corrected photographs do not always enable a technician to achieve a suitable match because natural teeth and restorative materials have different optical properties, and information such as the tooth shades, translucency and value are not revealed. What is needed is a method of transforming photographs that provides technicians with more information about the teeth to be matched than a digital photograph that has been nominally corrected for color.